I must admit, I am ignoring my own earlier assertions about not using non-standard fonts in presentations. PCs do not come with Helvetica installed, and I love it. In most cases, embedding the font inside the PowerPoint presentation makes sure that people can use it on other computers as well.
Helvetica is a relatively tame font. Selectively you can go a bit wilder. The image below (taken from the excellent Google LIFE image archive) mixed together with the Boycott font gives that instant jeans commercial effect. Here is an example of a presentation that uses something similar. Obviously, these type of fonts are only to be used for big image/huge font presentations, and probably not in every presentation you make.